In a nuclear fuel assembly for a boiling water reactor (BWR in the following specification), the full length fuel rods (FLFR in the following specification) are received between the base and the head of the fuel assembly with a small longitudinal gap allowing the FLFRs to expand in their longitudinal direction during operation of the nuclear reactor.
Usually, the upper ends of the FLFRs are retained by the head of the nuclear fuel assembly.
The partial length fuel rods (PLFR in the following specification) are used in BWRs for reasons of thermohydraulic stability and neutron moderation.
PLFRs extend upwardly from the base of the fuel assembly and stop at a distance from the fuel assembly's head. Usually, the length of the PLFRs is comprised between 25% and 75% of the length of the FLFRs.
The fuel rods are positioned and held longitudinally and transversally by a plurality of spacer grids spaced along the fuel rods. These spacer grids allow for local and limited sliding movement of the fuel rods in the spacer grids to accommodate the expansion of the fuel rods under irradiation.
Nevertheless, under specific operating conditions, the longitudinal holding force applied by the spacer grids to the bundle of fuel rods may not be sufficient to prevent a significant longitudinal displacement of PLFRs.
Accordingly, in order to prevent the PLFRs from lifting-off during nuclear reactor operation, PLFRs are usually attached to the base of the fuel assembly.
US-2008/0101528 discloses a fuel assembly. In this fuel assembly, the lower ends of the PLFRs are attached to the base through clamps which are integral with the base.
However, such an arrangement requires specific machining to achieve adequate tolerances for the clamps. Therefore, while such an arrangement is satisfactory, it is still desirable to simplify its design and lower its price.